The document discusses the difference between present participles ending in "-ing" and past participles ending in "-ed" when used with adjectives to describe a cause or receiver of a feeling. It provides examples of pairs of adjectives where the "-ing" form indicates the cause (e.g. "alarming") and the "-ed" form indicates the receiver of the feeling (e.g. "alarmed"). It then has users practice selecting the correct "-ing" or "-ed" form based on whether the subject is causing or receiving the feeling in example sentences.